Previously known diving helmets designed for use without a full diving suit are substantially all equipped with a flexible, stretchable neck seal. This seal, usually made of rubber or a similar substance, is attached to a metal, or other substantially rigid material, ring. The metal ring must be large enough so that a diver's head can pass therethrough. The metal ring in turn is attached in a waterproof manner to the helmet with securement latches of various types employed to hold the neck seal and its metal ring to the helmet.
Some previously known structures of this type were secured to the head of the diver by a head harness or a chin strap, or both. Some other diving helmets are held in place by means of cables or straps that are secured to the diver's body, then attached to the lower part of the helmet.
These known structures are difficult, if not impossible, to remove in an emergency if the pressure inside the helmet is lower than the surrounding pressure. The relative vacuum inside the helmet prevents the breaking of the seal between the neck dam (or seal) ring and the helmet. All previously designed neck ring locks merely release the seal and do not mechanically part (or break) the seal.
There are several causes for a lower pressure to occur inside a helmet. These causes include parting of the air supply hose above the diver, loss of air supply during descent and loss of air supply during inhalation, etc. While all helmets are equipped with a non-return valve whose function is to prevent lower pressure when the hose parts, these valves sometimes fail.
Previously known structures of this type require two hands or two or more operations to release the latches of the metal ring from secured engagement with the helmet. This requires considerable time and presents unnecessary complex requirements for removal of the associated helmet. Further, the small diameter end of the neck seal or dam engaged about the neck of the user of the helmet is subject to ballooning and the escape of air from within the helmet through the neck dam. Of course, should a diver be disposed in a head downward position when the neck dam balloons sufficiently to release air from within the helmet, water from the exterior of the helmet is free to flow into the latter, at least to some restricted degree.
Examples of previously patented helmets including some of the structural features of the instant invention are disclosed in U.S. Pat. Nos. 2,383,261, 2,664,567, 3,030,626, 3,172,126, 3,534,408, 3,729,744 and 3,806,950.